Gamma knife versus linear accelerator thalamotomy for essential tremor and Parkinson's disease: A systematic review and meta-analysis.

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Tremor, either in patients with Essential Tremor (ET) or Parkinson's disease (PD), constitutes the most common movement disorder. Stereotactic radiosurgery using Gamma Knife (GK) and linear accelerator (LINAC) systems, is an effective, incisionless treatment modality for ET and PD. Although these technologies have been used clinically since the 1990's, most studies have focused on GK, and efficacy, safety and time to treatment effect (latency) of GK and LINAC have not been compared. We therefore aimed to conduct a systematic review with network meta-analysis examining efficacy, adverse events (AEs) and latency of GK and LINAC for treating tremor in ET and PD. We conducted a systematic review with network meta-analysis in accordance with PRISMA guidelines, using the Embase and PubMed databases. We included all primary GK/LINAC thalamotomy studies in ET/PD patients with at least 6months of follow-up, reporting unilateral Fahn-Tolosa-Marin Tremor Scale (FTM-TRS) or Unified Parkinson's disease rating scale (UPDRS) scores pre-treatment/post-treatment and/or AEs and/or latency. The primary efficacy outcome was FTM-TRS Scale A or UPDRS Item 16 score reduction. AEs were presented as an estimated incidence, and latency as average time to first recorded clinical improvement in tremor. Six studies of 311 patients and 2 studies of 60 patients met inclusion criteria for GK/LINAC efficacy comparison, respectively. Network meta-analysis showed similar tremor reduction between modalities (standardized mean difference between pre- and post-treatment scores: GK: -2.18 (95% CI: -2.79, -1.57); LINAC: -2.13 (95% CI: -5.13, 0.87). GK also had a higher absolute AE rate, while LINAC was associated with a greater latency period. There was no correlation between GK efficacy and AE rate. Despite the relatively small sample sizes, these results demonstrate similar efficacy between GK and LINAC for ET and PD, with a trend toward higher efficacy but greater AE incidence and slower onset of tremor improvement in GK compared to LINAC.